In most model organisms in which it has been studied, low doses of ethanol have central nervous system- activating effects, whereas high doses are sedative. These acute effects of ethanol are commonly measured as changes in locomotor activity. Interestingly, a growing body of evidence suggests that the molecular, neurochemical, and neuroanatomical mechanisms that regulate ethanol's effect on locomotion are at least in part shared with those that underlie the drug's rewarding effects. For example, pharmacological and genetic manipulations have shown that midbrain dopaminergic pathways are involved in both the activating and rewarding effects of ethanol in rodent models. It is therefore likely that insights into ethanol's addicting effects can be obtained by studying the relatively simple effects of the drug on locomotor activity. The goal of this proposal is to study the genetic, molecular, and neural mechanisms that regulate ethanol- induced locomotor behaviors in Drosophila. Preliminary experiments have revealed that fruitflies show a biphasic locomotor response to ethanol similar to that observed in mammals, and that, as in rodents, dopaminergic systems play a role in ethanol's acute activating effects in flies. We propose to generate and characterize mutants with altered ethanol-induced locomotor activity. The genes disrupted by these mutations will be studied molecularly and their function will be analyzed in vivo upon establishment of transgenic flies. The brain regions that mediate ethanol's effect on locomotion will be mapped by selectively inactivating specific brain regions by means of targeted expression of a tetanus toxin-encoding transgene. The neurochemical profiles of these brain regions will be ascertained by determining the expression of neurotransmitters, the enzymes involved in their synthesis, and/or the receptor systems upon which they act. Together, these approaches will help us understand the basic molecular pathways and neural circuits that regulate ethanol-induced locomotor behaviors in Drosophila. Because the mechanisms of ethanol's action share common features in organisms as different as flies and mice, we predict that knowledge gained from Drosophila will provide novel and general insights into the processes by which ethanol acts in the nervous system to regulate behavior.